When individual herpes simplex virus (HSV) isolates are tested for their capacity to cause ocular infection in laboratory animals. It has been found that some isolates cause severe ocular disease whereas other HSV isolates cause little or no disease. The molecular mechanisms which account for differences in the pathogenesis of HSV isolates is not known. We have observed that HSV-1(17) replicated 100-fold more efficiently than HSV-2(186) within trigeminal ganglia of mice following ocular infection. In order to determine the molecular mechanisms responsible for these differences, we have constructed an intertypic recombinant (HSV-RD1) by exchanging nucleotide sequences within the DNA polymerase (pol) gene of HSV-2 (186) with DNA from the pol gene of HSV-1(17). Unlike HSV-2(186). D1 replicates within trigeminal ganglia of mice following ocular infection. The first objective of the proposal is to determine how the hybrid DNA pol gene of D1 increases the capacity of the virus to replicate within trigeminal ganglia following ocular infection. The number and location of HSV-(17) nucleotide sequences within the D1 pol gene will be determined by sequencing the DNA pol gene of HsV-1(17). HSV-2(186) and (D1) and then comparing the D1 pol gene sequence to the nucleotide sequence of the pol gene of its HSV-1(17) and HSV-2(186) parents. To determine if regulatory sequences upstream from the pol gene or if sequences coding for the amino acids of DNA pol play a role in the neuroinvasiveness of D1, we will construct hybrid DNA pol genes in vitro by exchanging either the promoter, the translational control region or the amino acid coding region of the HSV-1(186) pol gene with homologous regions from the pol gene of HSV-1(17). Hybrid genes will then be reintroduced into the HSV- 2(186) genome and the pathogenesis of the recombinants studies in vivo. We will determine how insertion of HSV-1(17) DNA into the HSV-2(186) gene for DNA pol alters the function of the enzyme by comparing pol gene expression in a neuronal and non-neuronal cell line infected with HSV- 1(17), HSV-2(186) and D1. Replacement of HSV-2(186) nucleotide sequences between m.u. 0.448 to 0.550 with corresponding HSV-1(17) DNA also generate intertypic recombinants which replicate within trigeminal ganglia following ocular infection. The second objective of the proposal is to determine a role of nucleotide sequences spanning m.u. experiments to find the smallest HSV- 1(17) fragment spanning m.u. 0.448-0550 which can rescue the neuroinvasive phenotype of HSV-(17) following transfection of this fragment with intact HSV-2(186) DNA. This fragment will then be sequenced in order to identify the HSV-1(17) nucleotide sequences responsible for enhancing the neuroinvasiveness of these intertypic recombinants. Information obtained from this proposal will identify molecular mechanism by which specific HSV-1 genes influence control over the capacity of HSV- 1 to replicate within the trigeminal ganglia following ocular infection.